The present invention relates to a puncture sealing agent capable of suppressing corrosion and damage given to steel cords of a tire and enhancing the sealing effect, while maintaining resistance to putrefaction of the sealing agent itself.
A known puncture sealing agent is, for example, injected into the inner space of a tire, and seals the damaged part from inside in case of puncture to keep airtight.
Hitherto, it is mainly composed of natural rubber latex, and contains ammonia at a high concentration of about 1.2 wt. % of rubber solid content to suppress solidification of latex and enhance stability in liquid state (liquid stability). In this composition, of impurities contained in natural rubber latex such as protein, fatty acid, other acetone extracts and ash content, the protein adsorbed on rubber particles is loaded with a strong negative electric charge in an alkaline state by addition of ammonia, and therefore rubber particles exist in the latex in a stable state without bonding each other. Moreover, ammonia transforms latex into an alkaline state, and oxidation and putre-faction of the protein can be suppressed, and thereby occurrence of malodour, degeneration, and deterioration are prevented.
Herein, the content of protein in natural rubber latex is usually expressed by a converted value on the basis of the nitrogen content measured by Kjeldahl method by multiplying this nitrogen content by 6.3 times, and conventional natural rubber latex contains protein equivalent to about 0.2 to 0.3 wt. % in the nitrogen content measured by Kjeldahl method.
According to Kjeldahl method, in a solid sample by evaporating water content, a decomposition promoter (mercury, mercury oxide, copper sulfate, etc.) is added, and the sample is pyrolyzed in concentrated sulfuric acid, potassium oxide, or sulfuric acid, fuming sulfuric acid, and nitrogen in the sample transformed into ammonium sulfate is quantitatively measured from this ammonium sulfate. Therefore, the ammonia added in the natural rubber latex disappears along with evaporation of water content before measurement. As a result, in Kjeldahl method, the nitrogen content in protein only is measured, without containing nitrogen in ammonia.
On the other hand, the content of ammonia in rubber latex is usually measured by a method specified in JIS K 6381, 5.3 (total alkali content), and conventional puncture sealing agent contains about 1.2 wt. % of ammonia according to this measuring method.
In the conventional sealing agent, however, although the liquid stability is enhanced by ammonia, it takes time to solidify and freeze the puncture damaged portion, and the sealing effect is insufficient. Still worse, ammonia may invade into the inside of the tire from the puncture damaged portion, and which may corrode steel cords used in the belt layer and carcass to lower the tire strength and durability. In addition, the stimulating smell of ammonia is a strong discomfort for the person handling the puncture sealing agent.
If the ammonia content is lowered, in particular, putre-faction of protein cannot be suppressed enough, and if other chemical is used as stabilizing agent instead of ammonia in order to maintain liquid stability, it is hard to expect to maintain satisfactory liquid stability and sealing performance.
It is hence an object of the invention to present a puncture sealing agent capable of preventing occurrence of stimulating smell or corrosive damage of steel cord due to ammonia, shortening the time to start cross-linking of rubber particles and solidify by stimulation of pressure or the like, and enhancing the sealing effect, without leading to putrefaction of protein if the ammonia content is less than 0.5 wt. %.
According to one aspect of the present invention, a puncture sealing agent for sealing an inner surface of a tire comprising a deproteinized rubber latex made by removing protein from a natural rubber latex, wherein nitrogen content is 0.1 wt. % or less of rubber solid content of the deproteinized rubber latex, and ammonia content is 0.5 wt. % or less of the rubber solid content.
Herein the nitrogen content is measured by the Kjeldahl method, and the ammonia content is measured by a method specified in JIS K 6381, 5.3.
Preferably, a surface active agent should be contained as stabilizing agent by 0.01 to 1.8 wt. % of rubber solid content in the puncture sealing agent, and it is particularly preferred to use potassium rosinate as stabilizing agent because rubber particles in latex start cross-linking by stimulation of pressure or the like to enhance the pressure sensitive characteristic which is the nature to solidify and freeze, thereby enhancing the sealing performance.